Antibody therapy for cancer involves the use of antibodies, or antibody fragments, against a tumor antigen to target antigen-expressing cells. Antibodies, or antibody fragments, may have direct or indirect cytotoxic effects or may be conjugated or fused to cytotoxic moieties. Direct effects include the induction of apoptosis, the blocking of growth factor receptors, and anti-idiotype antibody formation. Indirect effects include antibody-dependent cell-mediated cytotoxicity (ADCC) and complement-mediated cellular cytotoxicity (CMCC). When conjugated or fused to cytotoxic moieties, the antibodies, or fragments thereof, provide a method of targeting the cytotoxicity towards the tumor antigen expressing cells. (Green, et al., Cancer Treatment Reviews, 26:269–286 (2000), this and all other references cited herein are hereby incorporated by reference in their entirety).
Because antibody therapy targets cells expressing a particular antigen, there is a possibility of cross-reactivity with normal cells or tissue. Although some cells, such as hematopoietic cells, are readily replaced by precursors, cross-reactivity with many tissues can lead to detrimental results. Thus, considerable research has gone towards finding tumor-specific antigens. Such antigens are found almost exclusively on tumors or are expressed at a greater level in tumor cells than the corresponding normal tissue. Tumor-specific antigens provide targets for antibody targeting of cancer, or other disease-related cells, expressing the antigen. Antibodies specific to such tumor-specific antigens can be conjugated to cytotoxic compounds or can be used alone in immunotherapy. Immunotoxins target cytotoxic compounds to induce cell death. For example, anti-CD22 antibodies conjugated to deglycosylated ricin A may be used for treatment of B cell lymphoma that has relapsed after conventional therapy (Amlot, et al., Blood 82:2624–2633 (1993)) and has demonstrated encouraging responses in initial clinical studies.
Immunotherapy provides a method of harnessing the immune system to treat various pathological states, including cancer, autoimmune disease, transplant rejection, hyperproliferative conditions, and allergic reactions. The immune system functions to eliminate organisms or cells that are recognized as non-self, including microorganisms, neoplasms and transplants. A cell-mediated host response to tumors includes the concept of immunologic surveillance, by which cellular mechanisms associated with cell-mediated immunity, destroy newly transformed tumor cells after recognizing tumor-associated antigens (antigens associated with tumor cells that are not apparent on normal cells). Furthermore, a humoral response to tumor-associated antigens enables destruction of tumor cells through immunological processes triggered by the binding of an antibody to the surface of a cell, such as antibody-dependent cellular cytotoxicity (ADCC) and complement mediated lysis.
Recognition of an antigen by the immune system triggers a cascade of events including cytokine production, B-cell proliferation, and subsequent antibody production. Often tumor cells have reduced capability of presenting antigen to effector cells, thus impeding the immune response against a tumor-specific antigen. In some instances, the tumor-specific antigen may not be recognized as non-self by the immune system, preventing an immune response against the tumor-specific antigen from occurring. In such instances, stimulation or manipulation of the immune system provides effective techniques of treating cancers expressing one or more tumor-specific antigens.
For example, Rituximab (Rituxan®) is a chimeric antibody directed against CD20, a B cell-specific surface molecule found on >95% of B-cell non-Hodgkin's lymphoma (Press, et al., Blood 69:584–591 (1987); Malony, et al., Blood 90: 2188 (1997)). Rituximab induces ADCC and inhibits cell proliferation through apoptosis in malignant B cells in vitro (Maloney, et al., Blood 88 637a (1996)). Rituximab is currently used as a therapy for advanced stage or relapsed low-grade non-Hodgkin's lymphoma, which has not responded to conventional therapy.
Several cell surface molecules that participate in B-cell and T-cell activation are expressed predominantly in several hematopoietic-based cancers, such as leukemias and lymphomas. A significant number of these molecules, such as CD2 and CD48, belong to the Ig superfamily, which is involved in processes such as adhesion, migration, proliferation, differentiation, and effector function of leukocytes (de la Fuente, et al., Blood 90:2398–2405 (1997)). In vivo studies have shown that administration of CD2 and CD48 monoclonal antibodies can inhibit T-cell responses and prolong allograft survival (Gückel, et al., J. Exp. Med. 174:957–967 (1991); Qin, et al., J. Exp. Med. 179:341–346 (1994)). CD84 is a member of the CD2 family and is expressed on hematopoietic tissues and cells, primarily lymphocytes and monocytes (de la Fuente, et al., supra) and may play a role in leukocyte activation. A CD84 homolog, NTB-A, may function as a co-receptor in inducing Natural Killer (NK) cell-mediated cytotoxicity, and its function was significantly affected in the absence of an intracellular signaling protein, Src homology 2-domain containing protein (Bottino, et al., J. Exp. Med. 194:235–246 (2001)).
Active immunotherapy, whereby the host is induced to initiate an immune response against its own tumor cells can be achieved using therapeutic vaccines. One type of tumor-specific vaccine uses purified idiotype protein isolated from tumor cells, coupled to keyhole limpet hemocyanin (KLH) and mixed with adjuvant for injection into patients with low-grade follicular lymphoma (Hsu, et al., Blood 89:3129–3135 (1997). Another type of vaccine uses antigen-presenting cells (APCs), which present antigen to naive T cells during the recognition and effector phases of the immune response. Dendritic cells, one type of APC, can be used in a cellular vaccine in which the dendritic cells are isolated from the patient, co-cultured with tumor antigen and then reinfused as a cellular vaccine (Hsu, et al., Nat. Med. 2:52–58 (1996). Immune responses can also be induced by injection of naked DNA. Plasmid DNA that expresses bicistronic mRNA encoding both the light and heavy chains of tumor idiotype proteins, such as those from B cell lymphoma, when injected into mice, are able to generate a protective, anti-tumor response (Singh, et al., Vaccine 20:1400–1411 (2002)).
Thus, there exists a need in the art to identify and develop agents, such as peptide fragments, nucleic acids, or antibodies, that provide therapeutic compositions and diagnostic methods for treating and identifying cancer, hyperproliferative disorders, auto-immune diseases, and organ transplant rejection.